In nature there are a number of abundant natural fibers, i.e. cellulose, keratin, fibroin, chitin, collagen, etc. that are of use to many industries and for many applications but historically have been difficult to work with due to their insolubility in water and many common organic solvents. This natural insolubility, mainly due to strong inter- and intra-molecular bonding, has restricted the solvation and processing of these natural fibers to crude and/or chemically harsh and environmentally unfriendly methods. Current and common processing methods are capable of manipulating the natural polymers to form fibers, threads, films/gels, papers, and can in some cases digest the polymer to liberate naturally occurring nanoscale (elements having at least one dimension in the 1-100 nm range, and more broadly, under 1000 nm)-sized structures from the source material. However, due to the uncontrolled methods in which nanoscale sized particles of these natural fibers are currently produced, their ultimate utility is limited.
Several technologies have been developed to dissolve cellulose and the previously-mentioned natural fibers. Nanoparticles of cellulose have been produced in one of three ways: rod-like cellulose nanoparticles have been extracted from plants by acid hydrolysis (nanocrystals), by mechanical treatment leading to microfibrillated cellulose (MFC), and microbially-produced nanofibrils (bacterial cellulose, BC). The cellulose solvation-based processing methods discussed above are effectively the state of the art for the production of nanoscale natural polymer particles. These methods have a major commonality in that they utilize different pathways to break down natural polymers into smaller and smaller pieces until at least one dimension fulfills the definition of nanoscale. With regard to cellulose and the scope of patented cellulose nanoparticle processing, it is important to note that at no point do these processes direct or control the ultimate size and morphology (shape) of the polymer particles.
Like cellulose, keratin, silk fibroin, chitin, collagen, and any similarly-structured natural polymers are challenging to work with due to solubility issues. Previous work in this field teaches that cellulose, keratin, silk fibroin, chitin, and collagen can be processed using strong bases or acids. However, these methods are harsh and often derivatize the polymer. The most well-known method is the processing of cellulose to form cellulose xanthate solutions, typically used for the production of viscose-Rayon. Keratin has also been dissolved in dialkyl sulfoxides like dimethyl sulfoxide. All of these previously used methods of solvation degrade and derivatize the natural polymers, or use environmentally unsafe or exotic organic solvents. It is desired to have a means for dissolving cellulose and other natural fibers without severe degradation or derivatization.